The present invention relates to a process to prepare alkyl phenyl phosphates from a mixture comprising monophenyl dichlorophosphate and diphenyl mono-chlorophosphate.
A process to prepare alkyl phenyl phosphates is described in U.S. Pat. No. 2,504,121. Monalkyl diaryl phosphate esters are prepared by reaction of an alkylchloro-phosphate and a phenolate compound. The alkylchlorophosphate is formed in a preceding step by reaction of phosphorus oxychloride and an alcohol. The phenolate compound is formed by reaction of phenol compound and a base. U.S. Pat. No. 2,504,121 teach that the reaction of a phenyl chlorophosphate compound with an aliphatic alcohol is objectionable, as the reaction is difficult to control and excessive quantities of triaryl phosphates are formed.
A process to prepare alkyl phenyl phosphates is also known from U.S. Pat. No. 6,299,887. In this publication an alkyl phenyl phosphate, more specifically (2-heptylundecyl)diphenyl phosphate, is synthesised by reaction of diphenyl phosphoryl chloride with 2-heptylundecyl alcohol in the presence of a triethyl-amine catalyst and an acid amine scavenger. Similarly, U.S. Pat. No. 6,136,997 relates to undesired processes starting from diphenyl phosphoryl chloride. It is not disclosed or suggested to start with a mixture of monoalkyl phenyl phosphate and dialkyl monophenyl phosphate.